Oil can be one of the most versatile items you can carry.

You must rest one round per hour, and one day every 7, or suffer penalties.

Running out of food or water can kill you. Running out of torches or lantern oil is really inconvenient and makes getting out of a dungeon very dangerous, even if you have party members with infravision.

Every party should have at least one 50-foot rope amongst their combined equipment.

Not every character must carry the same gear. Consider the gear the party needs as a whole and distribute it in a logical manner.

Iron spikes and a mallet or hammer can be very useful and versatile. They can be used to wedge a door shut (or open), secure a rope, or even to create pegs on a wall or other vertical surface to facilitate scaling up, down or across that surface. (Hint: You can toss a few iron spikes to distract a rust monster.)